COMP: Use separate build path for fftw versions
COMP: Use separate build path for fftw versions

Each version of fftw that is build should use a build
directory that is unique to that version.

BRAINSia/ITK,Kitware/ITK,thewtex/ITK,hjmjohnson/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,malaterre/ITK,LucasGandel/ITK,thewtex/ITK,LucasGandel/ITK,LucasGandel/ITK,richardbeare/ITK,LucasGandel/ITK,BRAINSia/ITK,richardbeare/ITK,malaterre/ITK,malaterre/ITK,BRAINSia/ITK,vfonov/ITK,LucasGandel/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,Kitware/ITK,thewtex/ITK,BRAINSia/ITK,thewtex/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,hjmjohnson/ITK,malaterre/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,hjmjohnson/ITK,Kitware/ITK,richardbeare/ITK,richardbeare/ITK,vfonov/ITK,vfonov/ITK,richardbeare/ITK,vfonov/ITK,Kitware/ITK,malaterre/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,malaterre/ITK,thewtex/ITK,LucasGandel/ITK,vfonov/ITK,BRAINSia/ITK,vfonov/ITK,hjmjohnson/ITK,thewtex/ITK,malaterre/ITK,LucasGandel/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,thewtex/ITK,hjmjohnson/ITK,malaterre/ITK,BRAINSia/ITK,hjmjohnson/ITK,LucasGandel/ITK